The present invention relates to an amorphous film of composite oxide and a crystalline film of composite oxide for use as a transparent conductive film to be formed as an electrode in flat panel displays and the like, as well as to a method of producing an amorphous film of composite oxide, a method of producing a crystalline film of composite oxide, and a sintered compact of composite oxide.
An ITO (Indium Tin Oxide) film is characterized in low resistivity and high transmission factor, and can be microfabricated easily. Since these characteristics are superior in comparison to other transparent conductive films, an ITO film is being broadly used in various fields including for display electrode in a flat panel display. The deposition method of the ITO film in today's industrial production process is mostly based on the so-called sputter deposition method of performing sputtering using an ITO sintered compact as the target since the ITO film can be uniformly formed on a large area with favorable productivity.
In a flat panel display manufacture process using an ITO transparent conductive film, the crystallinity of the ITO film immediately after the sputtering is amorphous, and, in most cases, microfabrication such as etching is performed with the ITO film in an amorphous state, and thermal annealing is subsequently performed in order to crystallize the ITO film. This is because an ITO amorphous film is advantageous in terms of productivity in a large etching rate, and the ITO crystal film is superior in low resistivity and in heat resistance, and both advantages can thereby be enjoyed.
Although most of the film obtained by sputtering the ITO target is amorphous, a part of the film becomes crystallized. The reason for this is that some particles that adhere to the substrate due to sputtering have a high energy level, the temperature of the film becomes so high as to exceed the crystallization temperature due to the transfer of energy after the particles adhere to the substrate, and a part of the film consequently becomes crystallized although the crystallization temperature of the ITO film is approximately 150° C. and most of the film is amorphous since it will be at a temperature that is lower than 150° C.
If a part of the ITO film becomes crystallized as described above, such crystallized portion will remain as so-called etching residue during the subsequent etching process, and cause problems such as a short circuit, since the etching rate of that part will be lower than the etching rate of an amorphous portion by roughly double digits.
In light of the above, it is known that adding water (H2O) in addition to the sputter gas such as argon in the chamber during the sputtering process is effective as a method of prevention of the crystallization of the film and amorphisizing the entire film (for instance, refer to Non-Patent Document 1).
Nevertheless, the method of attempting to obtain an amorphous film by way of sputtering upon adding water entails numerous problems. Foremost, in many cases particles are generated on the film. These particles have bad influence on the flatness and crystallinity of the sputtered film. Since particles will not be generated if water is not added, the problem of generation of particles is caused by the adding water.
In addition, the concentration will gradually fall below the adequate concentration, and a part of the film will become crystallized since the water concentration in the sputtering chamber gradually decreases pursuant to the lapse of the sputtering time, even if it is initially an adequate water concentration.
On the other hand, however, if the concentration of the water to be added is increased in order to reliably obtain an amorphous film, the crystallization temperature upon crystallizing the film in the subsequent annealing process will become extremely high, which is a problem in that the resistivity of the obtained film will become extremely high.
In other words, if sputtering is performed upon adding water to amorphize the entire sputtered film, it is necessary to constantly monitor and control the water concentration within the chamber, however, this is extremely difficult and requires considerable time and effort.
To overcome the foregoing problems, a transparent conductive material as a stable amorphous material is sometimes used in substitute for an ITO film in that a crystalline film can be easily formed. For instance, with a sintered compact having a composition of adding zinc to indium oxide as the target, it is known that such a target can be sputtered to obtain an amorphous film, but the sputtered film obtained as described above is an extremely stable amorphous material and will not crystallize unless it is subject to a high temperature of 500° C. or higher.
Thus, it is not possible to attain the advantages in the production process of crystallizing the film and incomparably reducing the etching rate, and the resistivity of the film will be approximately 0.45 mΩcm, which is higher than the crystallized ITO film. Moreover, the visible light average transmission factor of this film is roughly 85%, and is inferior to an ITO film.
Also, there are the following patent documents and the like that are similar to the present invention in certain respects as a matter of form but different based on configuration and technical concept, and the outline thereof is explained below.
Patent Document 1 (Japanese Laid-Open Patent Publication No. 2003-105532) aims to achieve a high resistivity film for use in touch panels and the like, and describes a sputtering target in that nonconductive oxide is added to ITO as the means for achieving the foregoing object.
Although magnesium oxide and the like are described in the claims as examples of the nonconductive oxide, the Examples only describe silicon oxide as the nonconductive oxide. In addition, Patent Document 1 fails to provide any description regarding the crystallinity of the film during deposition and the crystallization of the film by way of subsequent annealing, and the film resistivity is extremely high at roughly 0.8 to 10×10−3 Ωcm, the technical concept and range differ from the present invention.
Patent Document 2 (Japanese Patent No. 3215392) aims to obtain an amorphous film that is superior in flatness and heat resistance even at a temperature that is higher than the crystallization temperature of ITO, and realizes an amorphous film even at a substrate temperature of 200° C. by increasing the additive concentration of magnesium (2.4% or more) as the means for achieving the foregoing object. However, since the magnesium concentration is high, the film resistivity is also high (based on the results of Example 1, the film resistivity is 7.9×10−4 Ωcm), and the film of Patent Document 2 has inferior characteristics as a transparent conductive film in comparison to the present invention.
Accordingly, Patent Document 2 differs from the present invention in that its technical concept does not aim to control the crystallinity or lower the resistivity of the crystallized film, and the concentration of the added magnesium is also high.
Patent Document 3 (Japanese Patent No. 3827334) aims to increase the density of the oxide sintered compact, and describes an ITO sintered compact containing 5 to 5000 ppm of one or more types of elements selected from five types of elements such as magnesium and the like in the ITO, and which satisfies various other conditions as the means for achieving the foregoing object. However, Patent Document 3 only relates to the characteristics of a sintered compact, and fails to provide any description concerning the definition or improvement of the film characteristics.
Patent Document 3 vaguely describes only the specific resistance of the film obtained by sputtering the foregoing sintered compact in the Examples, and merely shows that the specific resistance is slightly lower than film obtained from a standard ITO to which prescribed elements are not added.
Moreover, no correlation between the substrate temperature and the film resistivity can be acknowledged, and the film resistivity is still low even at 100° C. Thus, it is assumed that the film is crystallized. In other words, Patent Document 3 fails to provide any knowledge regarding the film crystallinity and the like, and the technical concept and range are different from the present invention.
Patent Document 5 (Japanese Patent No. 3632524), Patent Document 6 (Japanese Laid-Open Patent Publication No. 2003-055759), and Patent Document 7 (Japanese Laid-Open Patent Publication No. 2003-160861) describe a target in that magnesium in a prescribed concentration range is added to the ITO, and respectively describe magnesium oxide, magnesium carbonate, and magnesium indium as the magnesium raw material. However, Patent Document 5, Patent Document 6 and Patent Document 7 relate to methods of producing a target inexpensively, without cracks, and without arcing during the sputtering process in order to form a film having characteristics such as high resistivity and flatness for use in touch panels and the like, and fail to include any technical concept concerning characteristics such as the film crystallinity and film resistivity of the present invention, and the range is also different.    [Non-Patent Document 1] Thin Solid Films 445 (2003) p235 to 240    [Patent Document 1] Japanese Patent Laid-Open Publication No. 2003-105532    [Patent Document 2] Papanese Patent No. 3215392    [Patent Document 3] Papanese Patent No. 3827334    [Patent Document 4] Papanese Patent No. 3632524    [Patent Document 5] Japanese Patent Laid-Open Publication No. 2003-055759    [Patent Document 6] Japanese Patent Laid-Open Publication No. 2003-160861
As described above, the conventional technology which uses a sintered compact having a composition of adding zinc to indium oxide as the target is insufficient as a solution since it has drawbacks such as high film resistivity.
Moreover, the patent documents and the like that are similar to the present invention in certain respects as a matter of form such as including descriptions of adding magnesium to ITO do not give consideration to the problems indicated by the present invention, and simply aim to achieve the high resistivity of the film, the amorphous stability of the film, and the high densification of the target by adding magnesium. Thus, the foregoing patent documents and the like do not include the technical concept of controlling the crystallinity of the film or leveraging the low resistivity of the crystallized film as with the present invention.
In addition, if the effect of high resistivity is to be sought based on the concentration of the added magnesium and the like, the additive amount is too high, and, if the effect of high densification of the target is to be sought, the descriptions are limited to those concerning the characteristics of the target, and there are no descriptions on favorable film characteristics of the present invention or descriptions in the Examples regarding the production method and the like.